Cellulosic biomass is a vast source of renewable energy and an abundant substrate for biofuel production. As an alternative to corn-based ethanol, bioethanol can be generated from lignocellulosic (LC) sugars derived from cellulosic biomass of renewable and sustainable plant feedstocks. Energy of cellulosic biomass is primarily stored as the recalcitrant polysaccharide cellulose, which is difficult to hydrolyze because of the highly crystalline structure, and in hemicellulose, which presents challenges because of its structural diversity and complexity. Many microbes cannot natively ferment pentose sugars (e.g., xylose) from complex lignocellulosic biomass, which is composed of cellulose, hemicellulose and lignin fractions. Even when engineered to express the minimal enzymes from native pentose sugar-metabolizing organisms, S. cerevisiae cannot ferment xylose from innocuous lab media at industrially-acceptable rates. Laluce et al., Applied Microbiol. Biotech. 166:1908 (2012); Almeida et al., Biotech. J. 6:286 (2011). Xylose is a prevalent sugar in both woody and herbaceous plants and a major component of hemicelluloses. Bioconversion of both xylose and glucose is required for the production of cellulosic biofuels. To further complicate matters, plant biomass must be chemically, mechanically, or thermally pretreated prior to enzymatic hydrolysis ex situ in order to produce fermentable glucose and xylose monomers. Such pretreatment processes generate a diverse array of degradation products derived from plant cell walls, such as hemicellulose and lignin-derived acetate and aromatic molecules, many of which inhibit cellular metabolism in S. cerevisiae and induce microbial stress during hydrolysate fermentation. Taylor et al., Biotechnology J. 7:1169 (2012); Liu, Applied Microbiol. Biotech. 90:809 (2011). At present, little is known about how such inhibitors impact xylose fermentation, particularly under strict industrially relevant, anaerobic conditions where ethanol production is maximized.
In view of the current state of the biofuel industry, particularly ethanol production based on xylose-containing feedstocks, it can be appreciated that identifying genes related to enhanced biofuel production is a substantial challenge in the field. Accordingly, a need exists in the field to identify additional genes that influence biofuel production in yeast, and consequently engineer recombinant strains of yeast capable of increased biofuel yields from commonly-available feedstocks, including xylose-containing feedstocks.